Time Reversal Invariance Test in Very Slow Neutron Reactions

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Several experimental tests of parity violation in neutron resonance absorption reactions have been carried out by means of the capture gamma-ray measurement and neutron transmission method using polarized slow neutrons at Los Alamos and KEK in order to determine the weak matrix elements in hadron-hadron interactions. At Los Alamos the determination of weak matrix element has been performed with the help of statistical model of compound nucleus. The likelihood analysis has been done for mean-zero }Gaussian randam variables for the helicity asymmetries in many p-wave resonances interfered with several neighboring s-wave resonances. On the other hand, exit channel interference effects in capture gamma-ray reactions have been measured at KEK.The measurement of the term A_9・sigma_n^^*・k_<gamma>^^* has been made on the p-wave resonance (E_n=0.734eV) of ^<139>La, where sigma_n^^* is the neutron spin direction and k_<gamma>^^* is the direction of emitted gamma-rays. These measurements are usef … More ul to find out the sensitivity of the observables of the time reversal violation.Neutrons have been polarized using the polarized proton and ^3He filters. Protons in ethylene glycol with Cr^V complexes are polarized dynamically in 0.4K and 25KG.A new method of polarization has been developed, in which protons in pentacence-doped naphthalene have been polarized by means of laser excitation and dynamical polarization of a photo-excited triplet state of pentacene in room temperature and in liquid nitrogen temperature.^3He gas has been polarized by means of the optical pumping.It has been found that La nucleus in LaA1O_3, which is a very important nucleus for the test of time reversal invariance, can be polarized by means of the dynamical method. The polarization has been more than 20%.The depolarization of low energy polarized neutrons in holmium crystal has been measured and found not to be so large in the energy region higher than 20 eV.Therefore, the measurement of a 5-fold correlation parameter in the neutron transmission through holmium became feasible. Less